I. Field of the Invention
This invention relates to a process of producing optically active propionate derivatives. The optically active propionate derivatives are useful as herbicides or intermediates of herbicides.
II. Description of the Related Art
A process of producing racemic 2-(4'-(3"-chloro-5"-trifluoromethyl-2"-pyridyloxy)phenoxy)propionic acid is known and is disclosed in Japanese Laid Open Patent Application (Kokai) No. 119476/79). In this process, 4-(3'-chloro-5'-trifluoromethyl-2'-pyridyloxy)phenol and sodium hydroxide are mixed in toluene at 60.degree. C., then 2-chloropropionic acid is added to the mixture at 50.degree.-80.degree. C. and then the resulting mixture is allowed to react at 110.degree. C. for 1-1.5 hours.
However, if this process is applied to the production of optically active (2R)-2-(4'-(3"-chloro-5"-trifluoro-2"-pyridyloxy)phenoxy)propionic acid, the yield is only 67% and the optical purity of the product is as small as 56%. Further, since (2S)-2-chloropropionic acid used as a starting material is relatively unstable, this material should be prepared immediately before use by hydrolyzing (2S)-2-chloropropionic acid methyl ester which is industrially available, so that the operation is troublesome.
On the other hand, a process of producing optically active (2R)-2-(4'-(3"-chloro-5"-trifluoromethyl-2"-pyridyloxy)phenoxy)propionic acid is known and disclosed in, for example, U.S. Pat. No. 4,532,328. In this process, methanesulfonate of (2S)-lactic acid and 4-(3'-chloro-5'-trifluromethyl-2'-pyridyloxy)phenol are reacted in N,N-dimethylsulfoxide in the presence of potassium carbonate at room temperature for 42 hours.
However, with this process, only a product with an optical purity of as low as 66% e.e. can be obtained.
A process of producing propionate derivatives is also known and is disclosed in Japanese Laid Open Patent Application (Kokai) No. 116986/88. In this process, methyl (2S)-2-chloropropionate, hydroquinone and 4-(3'-chloro-5'-trifluoromethyl-2'-pyridyloxy)phenol are used as starting materials and an optically active propionate derivative is prepared therefrom through several steps. Then the obtained optically active propionate derivative is converted to an acid chloride with thionyl chloride, and the acid chloride is reacted with tetrahydrofurfuryl alcohol to obtain the desired product.
However, with this process, since the desired product is obtained after forming optically active (2R)-2-(4'-(3"-chloro-5"-trifluoromethyl-2"-pyridyloxy)phenoxy)propionic acid, two steps are required for obtaining the desired product. Further, since the thionyl chloride used in this process has a tendency to vigorously react with water to decompose, the handling of the substance is troublesome in the industrial scale.
Thus, a process of producing optically active propionate derivative which is simple in operation and by which the desired product with high optical purity may be obtained is needed.